Oil country tubular goods casing coupling

ABSTRACT

A threaded coupling comprising a first end, a second end, a first portion of the threaded coupling defining a first thread profile, a second portion of the threaded coupling defining a second thread profile different from the first thread profile, where at least two threads of the second thread profile proximate to the second end are reduced in height according to an extra machining angle.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNo. 62/578,941, filed on Oct. 30, 2017; the contents of which are herebyincorporated by reference in their entirety.

FIELD

The present invention relates to apparatuses and methods related to acasing coupling which may be used in drilling oil and gas wells.

BACKGROUND

Oil and gas wells and other types of wells, such as geothermal wells,are typically drilled from the well surface to a desired downholelocation using a rotary drilling rig, drill pipe, and drill bits. Casingis used as a structural retainer and conduit in those wells.

Wellbores for producing oil, gas, or other formation fluids aretypically drilled in stages. For example, a wellbore may be firstdrilled with a drill string and a first drill bit having a particulardiameter. At a desired depth for a first portion of the wellbore, thedrill string and drill bit are removed from the wellbore. Tubularmembers of a smaller diameter, often referred to as casing or a casingstring, may then be placed in the first portion of the wellbore. Anannulus formed between the inside diameter of the wellbore and theoutside diameter of the casing string is generally filled with cement.The cement provides support for the casing and isolates downholeformations or subterranean strata from each other.

Often, the next step in drilling the wellbore is to pass the drillstring with a second, smaller diameter drill bit through the firstcasing string and drill another portion of the wellbore to a selecteddepth beyond the depth of the first casing string. This sequence ofdrilling wellbores and installing casing strings may be repeated as manytimes as necessary, with smaller and smaller components until theultimate desired depth or downhole location of the wellbore has beenachieved.

Most wells in North America are also drilled horizontally and latercompleted—hydraulically fractured—through the casing. Horizontal wellsmay require the casing to be rotated, to reduce pipe-wellbore frictionand to prevent the casing string from buckling and sticking due tofriction induced compression loads, thereby allowing the string to berun to its total depth. Rotation results in casing string torque.Hydraulic fracturing can place high internal pressure and tensionloads—resulting from ballooning and thermal effects in addition tostring weight—on casing strings.

Wells may require thousands of feet of casing. For example, a wellboremay be drilled to a depth of 10,000 feet and further drilledhorizontally another 10,000 feet, if hydraulic fracturing completionsare implemented. As such, multiple pipe segments are connected togetherto form the casing string, and the pipe segments are connected throughthreaded couplings. Many of the specifications of couplings (“boxes”)and pipe segments (“joints”) are standardized by the American PetroleumInstitute (“API”). Casing connections comprised of API couplings havelow torque capacity relative to the pipe.

Oilfield couplings must meet strength specifications in order tomaintain the mechanical integrity of the casing string. The strength ofthe couplings is particularly tested greatest whenever the casing stringis used for hydraulic fracturing completions. Most casing stringfailures occur in connections. As such, there is a need within the artfor strong and reliable couplings that can be manufactured economically.

BRIEF SUMMARY

The disclosed embodiments relate to a threaded coupling comprising afirst end, a second end, a first portion of the threaded couplingdefining a first thread profile, a second portion of the threadedcoupling defining a second thread profile different from the firstthread profile, where at least the first two threads of the secondthread profile proximate to the second end are reduced in heightaccording to an extra machining angle.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of a cross-section of a coupling accordingto an exemplary embodiment.

FIG. 2 illustrates a schematic drawing of a top portion of thecross-section of the coupling according to an exemplary embodiment.

FIG. 3 illustrates a schematic drawing of a buttress thread shape of thecoupling according to an exemplary embodiment.

FIG. 4 illustrates a schematic drawing of a relief groove located at amidsection of the coupling according to an exemplary embodiment.

FIG. 5 illustrates a schematic drawing of an end portion of the couplingwith a machining angle according to an exemplary embodiment.

FIG. 6 illustrates a schematic drawing of a coupling connecting totubular pins according to an exemplary embodiment.

FIG. 7 illustrates a permanent marking indicating a second end (millside) of the coupling according to an exemplary embodiment.

DETAILED DESCRIPTION

Preferred embodiments of the invention and its advantages are bestunderstood by reference to FIGS. 1-7 wherein like numbers refer to sameand like parts.

The term “oil country tubular goods” and “OCTG” are used in thisapplication to include casing, tubing, pup joints, couplings, and anyother type of pipe or tubular members associated with drilling,producing, or servicing oil wells, natural gas wells, geothermal wellsor any other subsurface wellbore.

A variety of oil country tubular goods (OCTG) and widely used casingaccessories may be engaged with each other by threaded connectionsformed in accordance with the teachings of the present invention. Forsome applications, tubular members may be sections of a casing stringused to both drill and complete a wellbore (not expressly shown).

Referring to FIG. 1, a coupling 50 may have a shorter length, the sameoutside diameter, and most thread element dimensions and configurationassociated with standard API couplings for oil country tubular goods.The coupling 50 may be described as a relatively short section of tubethat can be defined in part by a first end 51 and a second end 52 with alongitudinal bore 54 extending there between.

According to an exemplary embodiment, the coupling 50 can include afirst internal thread profile 61 and a second internal thread profile 62formed within the longitudinal bore 54 extending respectively from thefirst end 51 and the second end 52. In some embodiments, the firstinternal thread profile 61 and a second internal thread profile 62 canbe mirrored. Center plane or midsection 56 can define approximately amiddle of the coupling 50 defining a relief groove 92. For someapplications, the first and second internal thread profiles 61 and 62may comprise buttress threads for OCTG.

Referring still to FIG. 1, the first internal thread profile 61 (fieldside) may have a different pitch diameter than a pitch diameter of thesecond internal thread profile 62 (mill side). Therefore, the coupling50 may include a first pitch diameter and a second pitch diameter. Thepitch diameter of the second internal thread profile 62 may be smallerthan the pitch diameter of the first internal thread profile 61, thepurpose of which is to ensure that the mill side has higher make-uptorque. Said differently, a crest diameter of the second internal threadprofile 62 may be smaller than a crest diameter of the first internalthread profile 61.

FIG. 2 illustrates that a first portion 57 of the coupling 50 closer tothe first end 51 may have a first taper 71, and a second portion 58 ofthe coupling 50 closer to the second end 52 may have a second taper 70.According to an exemplary embodiment, the taper 71 of the first portion57 and the taper 70 of the second portion 58 can have the same or asimilar taper angle. Thus, the taper 71 of the first portion 57 can bethe same as the taper 70 of the second portion 58. In the embodimentswhere the taper 71 of the first portion 57 is the same as the taper 70of the second portion 58, the taper 71 of the first portion 57 can passthrough different points than the taper 70 of the second portion 58because the pitch diameter of the threads 62 associated with the secondportion 58 can have a smaller crest diameter than the threads 61associated with the first portion 57.

Respective internal thread profiles 61 and 62 may be formed on firstportion 57 and second portion 58 using threading machines and equipment(not expressly shown). In addition, the coupling 50 may engage with oneor more pins.

Various types of powered tools and equipment (not expressly shown) maybe used to engage coupling 50 with a first pin 20 a (FIG. 6). In asimilar manner, the coupling 50 may engage with a second pin 20 b. Thefirst pin 20 a may engage the coupling 50 by engaging the threads of thefirst portion 57, and the second pin 20 b may engage the coupling 50 byengaging the threads of the second portion 58 (See: FIG. 6). The firstpin 20 a may engage the first internal thread profile 61 having thefirst pitch diameter, and the second pin 20 b may engage the secondinternal thread profile 62 having the second pitch diameter. Accordingto an exemplary embodiment, the first pin 20 a and the second pin 20 bmay be substantially similar in design and construction. The second pin20 b may engage the coupling 50 at a factory during manufacture (themill pin), which may engage the second portion 58 (mill side) of thecoupling 50; the first pin 20 a may engage the coupling 50 at thewellsite (the field pin), which may engage the first portion 57 (fieldside) of the coupling 50.

FIG. 6 shows the first and second pin 20 a, 20 b as generally having anelongated, hollow section of casing with a longitudinal bore 24. Thefirst and second pins 20 a, 20 b may also include thread profiles. Therespective thread profiles of the pins 20 a, 20 b may have the same orsimilar pitch diameters.

Extreme end 30 a of the first pin 20 a (i.e. “field end”) and extremeend 30 b of the second pin 20 b (i.e. “mill end”) may be in directcontact with each other at the midsection 56 of the coupling 50. Thiscontact between the extreme ends 30 a and 30 b can create adjoining orabutting radial torque shoulders located proximate to the midsection 56of coupling 50. Direct contact between extreme ends 30 a and 30 b canensure that axial compressive loads and most torsional loads exertedduring casing string running and rotation will be transmitted againstadjacent tubular members 20 a and 20 b rather than the adjacent threadflanks of the coupling 50. In this way, the coupling 50 may not includea shoulder or ring between the first and second pins 20 a, 20 b.

In some embodiments, the coupling 50 can include a groove, symbol, orother permanent marking 95 externally located only on the mill end(second section 58) of the coupling 50 (See FIGS. 2, 6, and 7). Becauseof the different pitch diameters, the coupling 50 should indicate whichend 51, 52 is the mill end. The groove, symbol, or other permanentmarking 95 can be etched or machined into the mill end of the coupling50 during manufacturing.

Referring again to FIG. 2, the coupling 50 may comprise J55, K55, N80,L80, C90, R95, T95, P110 or C110 coupling stock. When P110 couplingstock is used, the P110 coupling stock can have a lessened tensilestrength than standardized P110 tensile strength. The tensile strengthof the coupling stock may be lessened through a heat treatment.

As shown in FIG. 2, the second portion 58 may include a taper angle 70and an extra machining angle 72. In some embodiments, the first portion57 may similarly include a taper angle 71 and an extra machining angle,but the preferred embodiment performs the extra machining angle 72 onlyon the mill end. In some embodiments, the extra machining angle 72 maybe different than the taper angle 70 of the second portion 58.

The pitch diameters 62 and 61 can decrease according to the taper angle70 from the first or second end 51 or 52 toward the midsection 56.According to an exemplary embodiment, the extra machining angle 72 mayaffect the first 3-5 threads of the thread profile 61 or 62. The extramachining angle 72 may be performed at an angle approximately 1-5°higher than the taper angle 70. For example, if the taper angle 70 is5°, then the extra machining angle 72 can be 10°. As shown in FIG. 5,the extra machining angle 72 causes the height of the threads 90 closestto the ends 51, 52 to be shortened according to the extra machiningangle 72. The crests of the threads 90 closest to the ends 51, 52 arealso angled according to the extra machining angle 72, but the roots ofthe threads 90 closest to the ends 51, 52 are cut at the taper angle 70,71. The number of threads machined at the extra machining angle 72 canbe the 2-5 threads closest to the ends 51, 52. The extra machining angle72 may be generated by causing another machining pass before forming thepitch diameters 61, 62.

The effect of the extra machining angle 72 reduces stress on the lastthread of the coupling 50, which is usually the thread that receives themost stress. Reducing the stress on the last thread reduces the chancesof failure within the coupling 50.

Referring to FIG. 3, a close-up of the buttress thread profile 80 isillustrated. As shown, each buttress thread may include a stabbing flankand a load flank. The stabbing flank may be closer to the midsection 56than the load flank. The load flank of the thread shape 80 can carry theload of a casing string.

FIG. 4 illustrates the relief groove 92. In some embodiments, the reliefgrove 92 creates a reservoir for trapped thread compounds and can allowfor economy by eliminating the need for a perfect land of threads duringmanufacturing.

Although a few embodiments have been described in detail above, othermodifications are possible. For example, the logic flows described abovedo not require the particular order described or sequential order toachieve desirable results. Other steps may be provided, steps may beeliminated from the described flows, and other components may be addedto or removed from the described systems. Other embodiments may bewithin the scope of the invention.

From the foregoing, it will be observed that numerous variations andmodifications may be effected without departing from the spirit andscope of the invention. It is to be understood that no limitation withrespect to the specific system or method described herein is intended orshould be inferred. It is, of course, intended to cover all suchmodifications as fall within the sprit and scope of the invention.

What is claimed is:
 1. A threaded coupling comprising: a first end; asecond end; a first portion of the threaded coupling defining a firstthread profile; and a second portion of the threaded coupling defining asecond thread profile different from the first thread profile, whereinat least two threads of the second thread profile proximate to thesecond end are reduced in height according to an extra machining angle.2. The threaded coupling of claim 1, wherein the threaded couplingcomprises J55, K55, N80, L80, C90, R95, T95, P110 or C110 couplingstock.
 3. The threaded coupling of claim 2, wherein the threadedcoupling comprises P110 coupling stock, and wherein the P110 couplingstock comprises a lessened tensile strength than standardized P110coupling stock.
 4. The threaded coupling of claim 3, wherein the P110coupling stock is lessened through a heat treatment
 5. The threadedcoupling of claim 1, wherein the first thread profile comprises a firsttaper angle.
 6. The threaded coupling of claim 5, wherein the secondthread profile comprises a second taper angle, and wherein the secondtaper angle is substantially the same as the first taper angle.
 7. Thethreaded coupling of claim 1, further comprising a relief groove formedat a midsection of the threaded coupling.
 8. The threaded coupling ofclaim 1, further comprising: a first pin engaged to the first threadprofile; and a second pin engaged to the second thread profile.
 9. Thethreaded coupling of claim 8, wherein a first end of the first pin is indirect contact with a first end of the second pin at approximately amidsection of the threaded coupling.
 10. The threaded coupling of claim1, wherein the extra machining angle is larger than a taper angle of thesecond thread profile.
 11. The threaded coupling of claim 1, wherein thesecond end is a mill end of the threaded coupling, and furthercomprising a permanent marking indicating the mill end formed on anexterior of the threaded coupling.
 12. A system comprising: a threadedcoupling comprising: a first coupling end a second coupling end; a firstportion of the threaded coupling defining a first thread profile; and asecond portion of the threaded coupling defining a second thread profiledifferent from the first thread profile, wherein at least two threads ofthe second thread profile proximate to the second coupling end arereduced in height according to an extra machining angle; a first pinengaged to the first thread profile; and a second pin engaged to thesecond thread profile.
 13. The system of claim 12, wherein the threadedcoupling comprises J55, K55, N80, L80, C90, R95, T95, P110 or C110coupling stock.
 14. The system of claim 13, wherein the threadedcoupling comprises P110 coupling stock, and wherein the P110 couplingstock comprises a lessened tensile strength than standardized P110coupling stock.
 15. The system of claim 14, wherein the P110 couplingstock is lessened through a heat treatment.
 16. The system of claim 12,wherein the first thread profile comprises a first taper angle, whereinthe second thread profile comprises a second taper angle, and whereinthe second taper angle is substantially the same as the first taperangle.
 17. The system of claim 12, further comprising a relief grooveformed at a midsection of the threaded coupling.
 18. The system of claim12, wherein the first portion extends between the first coupling end anda midsection of the coupling, and wherein the second portion extendsbetween the second coupling end and the midsection of the coupling. 19.The system of claim 12, further comprising a permanent markingexternally etched on a mill end of the threaded coupling.
 20. A methodfor manufacturing a threaded coupling comprising: forming a first threadprofile on a first portion of the threaded coupling; forming a secondthread profile, different from the first thread profile, on a secondportion of the threaded coupling; and reducing in height at least twothreads of the second thread profile proximate to a second end of thethreaded coupling according to an extra machining angle, wherein theextra machining angle is higher than an angle defining the second threadprofile.